Acquisition and Communicability

The origin of PrPres in any given mammal is thus critically important. There are several ways by which it may arise. In humans, PrPc may spontaneously change into PrPres, or inheritance of a defective gene that codes PrPc may cause the prion protein to be abnormally shaped. Finally, acquired cases may occur when PrPres from an infected mammal is introduced into a susceptible mammal through contaminated central nervous system tissue. In animals the origin of PrPres is thought to be acquired only. In humans or animals, there is a dynamic pathogenic process that occurs for acquired cases. The process can be broken down into distinct phases of infection and peripheral replication, CNS neuroinvasion, and neurodegeneration (94,96).